One of my neon tetra appears to have gill damage - came with it from the pet store. I believe this to be true because unlike the other tetra, his gill is red around the bottom part. No visible bleeding. I've had him for several weeks and despite his gill having some damage, he behaves normally as far as I can tell.

Is there something that I can do to heal this or is this a permanent damage? The fish in question lives in a 55 gallon tank with 3 other neon tetra, a male and female swordtail, a black molly, and 4 clown loaches.

Bonus question: all of my neon tetra open and close their mouths when they swim repeatedly. I've only just recetly noticed this behavior. One of the tetra (not the damaged gill one) does this more exagerattedly than the others. Is this an alert that there is another problem going on with my tetra or is this normal neon tetra behavior? I have read about neon tetra disease and do not believe they have that at all.

If it came like that from your lfs i dont think there is much you can do except keep an eye on it, and medicate it if i gets any worse. You could add a little pimafix, just to be safe. There could have been a problem with the shipment of the tetra, maybe the bags overheated or something, i know that can cause gills to turn red. Also, what are the parameters of your tank? I'm not realy experienced with tetras, so someone else will have to help you with your bonus question, sorry.

I assume you're using test strips to test (since you mentioned the "safe zone"). Those tests can be highly inaccurate. You're much better off getting the AP Freshwater Master Test Kit (which uses liquid test reagents). In the meantime take some water to the LFS and ask them to test your water for you. If the tank is relatively new then I'm assuming its not finished cycling. You can really help out by answering the questiosn in the sticky I mentioned.

1~What type of fish is afflicted? Neon Tetra - gill damage red around the bottom part of the gill.
2~What are your tank parameters (ammonia, nitrites, nitrates, temp, pH)?
ammonia - .15
Nitrate - 10 ppm
Nitrite - 0 ppm (none detected from the test)
Hardness - 75
alkalinity - ~40
pH- 7.1
temp - stable at 80 degrees
3~ How large is the tank? How long has the tank been set up? 55 gallons, about a week and a half. the fish in question was transfered to the 55 gallon tank from a 10 gallon tank after test reads on the 55 gallon tank showed the tank was stable for 3 days in a row.
4~What type of filtration are you using? A top fin filter that the tank came with - it has a tube that draws water into it and two cartrigdes that filter the water out. I also use a gravel cleaner when I do the 20% water changes.
5~How many fish are in the tank? What kinds of fish are they and what are their current sizes? 1 pregnant black molly, a male and female swordtail, 4 small clown loaches, 4 neon tetra
6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time? Once, I intend to do this every week and I remove 20-25% water at a time depending on the nitrate levels. I do 10% changes if there's something real wonky going on with a test, but so far I haven't had to do that.
7~How long have you had the fish? If the fish is new, how did you acclimate it/them? I've had the fish for about a month. I put him in my already established 10 gallon tank with the other tetra. When moving him to the 55 gallon tank, I did so responsibly as far as water tests go. The tank has remained stable, too.
8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.? He has changed environments, but his condition was there before changing him to the 55 gallon tank. The 55 gallon tank does have bubble rocks where the 10 gallon didn't have any at all.
9~What kind of food have you been feeding your fish, have you changed their diet recently? tetra min tropical flakes.

bonus question: why do the tetra move their mouths when they swim and also is this normal tetra behavior or an alert that there's something more wrong with my tetra that also needs to be looked at? They do not have neon tetra disease.

PS reason I didn't fill this out at first was because I just wanted to know what to do with a damaged gill (that was caused before purchasing him) and also if the opening and closing of the mouths repeatedly was normal tetra behavior or not.

Thanks. Ok, it looks like the 55 isn't finished cycling yet. Did you transfer any of the filter material or gravel from the 10 gallon tank to the 55 ? That will help speed up the cycle tremendously.

If the gills are red on both sides I would suspect ammonia poisoning. If its only one side and he's eating and acting normally then it could just be an old injruy. Watch to see if it gets infected - if its been that way for month I would worry to much.

I'm more concerned with the "bonus question". That could be a reaction to the ammonia. I only have one remaining neon tetra and he does open and close his mouth alot also. I too thought this was because my tank wasn't finished re-cycling after the medications I had to put in it a few weeks ago. Keep watching your tank parameters and be ready to do water changes if they go above 0.5ppm for ammonia or nitrites. Take some of the filter material off the 10 gallon (assuming there are still fish in it) along with some of the gravel and move it to the 55G. Put the 10G's filter material into the Top Fin filter cartridge (where you would normally put the activated carbon).

Thats the best I can offer - someone who's had success at keeping neon's may pipe in later.

Yes, I added about 5 gallons of water from my already established tank at first before I added the fish several days later. I also tossed in a small handfull of gravel from the already established tank as well. When I transferred the fish, I did so by putting all of them in a bag with their current water in it and then let them sit in the new tank for a while in the bag, then let them all out with the water in the bag, so I got even more water from the old tank into the new tank. I beleive more in a fishless cycle, but I'm so terribly impatient.

The damage is only on one side and it has been that way since purchasing him. I wonder about the mouth movement. I'll do some research through google on that and see if I come up with anything myself. It could just be normal tetra behavior. They do not appear to need more oxygen in their water and I do not suspect ammonia poisoning as my daily test show that ammonia is in safe levels.

Hi again Go grab some more gravel and some of the filter material from the 10G. There is very little of the good bacteria we want in the water column - most of it lives in the filter and in the gravel and non decorations.

Let me know if you find anything on the neon mouth breathing. Personally I've found neon's VERY difficult to keep alive, which is why I only have 1 left